Method of casting diamond core drill bits



i Patented Feb. 121,

NITE STATES METHOD or OAS'IING'DIAMOND CORE mun, BITS Warren SLJamar and Edward H. Dodd, Duluth,

Minn 'assignors to, B 8. Application March 18,

4 Claims.

. This invention relates to themanuiacture of diamond core drill bits, and particularly to a novel method of exactly positioning and securely fixing diamonds, bortz or carbonados within the cutting faceand/or bit. The principal object of the invention is to produce such a bit durability.

Another object is that of readily producing a.

plurality of such drills, orportions thereof (as in a fabricated bit) of as uniform and identical shape and other essential characteristics as possible, this being so essential in the art of diamond core drilling where successive useof like drills is necessary. I

- A further object of the invention is that of providing a more secure setting than heretofore known vfor each stone, and'that regardless of :irregularities in the shape of the respective stones.-

Still another object of the invention is that of permitting the secure setting of exceedingly cated mold and a drill head as it would appear formed therein.

Figure 2 is a plan view of one-quarter of the base plate of themold with one arrangement of depressions forthe diamonds therein. I

Figure 3 is a perspective view of a. fractional die portion of bit just prior to ultimate finishing, or a die used in making the wax intaglio. Figure 4 is a plan view of the face of modified form of core drill bit.

Figure 5 is a side elevation of Figure 4. Since the invention is not to be limited to any speciiic'abrasive, wherever, in the following description, the words diamonds, bortz, or carbonados", are used, the meaning is that either of these, or any otherv suitable abrasive for the purpose, maybe used, in-the forming of the bit. The general practice of setting carbonados and/or larger bortz in what are known as diamond core drill bits is for the setter to insert the stones individually into holes which he has cut into faces of such. a core drill having maximum efllciency and a slightly Patrick, Duluth, Minn. 1938, Serial No. 190,123.

(or 'zc-ms) the bit metal so that each stone'will be at the required location and will provide exactly the desired clearance. In this task, it is essential that the setter so fashion a hole that it will conform exactly to the shape oi the stone to be set into it and take into consideration exactly the surfaces of the stone which he desires to expose. In such casejit is the usual practice to line the holes with copper or other soft metal to serve .as a cushion and the bit metal is then drawn snugly. around each stone by caulking with small tools, designed for the purpose.

While this form of setting is rapid and is setisfactory for black diamonds, or carbonados, because of their size, it is not satisfactory for or as applied to many sizes and varieties of bortz. Due to its brittleness, and the fact that it possesses no abrasive qualities other than afforded by a scratching action, the successfulruse of bortz depends upon the insertion of many cutting points aspossible in a bit, leading to the practice of employing much smaller bortz than are usually used in carbons. The practice of setting small bortz by hand is not dimcult when confined to whole; almost spherical stones, which vunfortunately. constitute a very small part of bortz pro- 'duction. There are, however, quite large quantitles 'of equally desirable bortz from the standpoint of quality which cannot be satisfactorily set by hand, owing to great irregularity in shape; likewise, due to natural brittleness, there is great hazard of causing damage to the bortz in attempting to solidly-imbed them in the bit metal by the caulking process; also by reason of the space required to permit hand caulking, the number of stonesioi a given size which may be insertedinto a bit is curtailed. The principal ob- Jection to hand setting as applied to small bortz in the sizes most desirable for core drill usage is the great difliculty of properly imbedding this material, particularly if irregular shapes are employed. a By means of our process we are able to more solidly imbed each stone than'is possible in hand setting and more accurately locate each stone'so as to give exactly the clearance required; also it permits the use of stones of irregular shape equally eflicient in drilling, but not suitable for hand setting; also it permits exposing exactly that portion of each stone that is wanted, regard: 0

less of its shape, and which is frequently not possible otherwise. v I H -In carrying out the stepsof this process in the forming of a drill bit havinldiat'onds 'oiffair size in the working face thereof, first a suitable iii die forming mold is provided, the one here illustrated being of fabricated construction, the bottom plate thereof being shown at I, it being separable from the other parts of the mold, particularly for convenience in forming the pattern for the face of the bit thereupon. This bottom plate has an'annular trough formedtherein, as indicated in Figure 1, and in the bottom of this trough is then laid out a pattern of the desired locations of the diamonds, a. quarter of such being clearly shown in Figure 2 of the drawing, and in which the desired location of each diamond is determined. Then there is formed as by drilling or otherwise, at each such location, a depression 2, those adjacent both the inner and outer circumferential edges being so positioned as to cause the diamonds when placed to protrude radially the proper distance to provide the exact clearance desired for the bit when drilling.

After this pattern is completed and the depressions formed therein as desired, of course to accommodate the size of diamonds being employed,

the mold may be completely assembled, properly positioning upon the face plate I the metal cylinder or outer portions 3 of the mold as well as the core 4, these being of a size and spaced in respect to the positioning of the diamonds so as to correspond exactly with the pattern made on the base plate trough. The inner and outer walls of the annular trough are fluted their entire depth with small slots or grooves leading upwardly from the position of each marginal or clearance diamond which results in similarly shaped ribs leading from each such marginal diamond, and which projecting ribs are subsequently removed from the walls of the finished bit as for example in a turning lathe, thus providing ample clearance intermediate of the marginal diamonds, as well as intermediate of the 'outer wall of the drill and inner wall of the hole being drilled and about the core being formed by the drill.

These parts of the mold may be firmly held together in any desired manner either for making the template die or the final drill bit.

A template or die is then made, and is preferably produced in the form of a casting of bronze or other suitable metal in the above described mold. However this die may be made manually or otherwise shaped according to plans of the desired bit face, and is used in making an impression or intaglio of the face of the mold in suitable wax or other plastic adhesive suitable for the purpose, such as dental or electrotypers wax.

Now the diamonds or bortz, or whatever abrasive is to be cast into the bit. after being sorted or screened to the desired size, are treated to render them electrically conductive, preferably for example, witha suitable coating of silver, such as used on mirrors or the like, 'or a coating of brass or bronze powder. These thus treated stones are then placed individually each into a depression in the wax impressions, and, after all the stones are so placed, a'metal binder film of 7 copper, nickle, or other suitable metal is formed intermediate of and wholly about the entire portion of said stones extending above and free from the wax, by a suitable electroplating process.

This relatively thin metal binder carrying the stones protruding from the face thereof is then removed from the wax and placed within the original mold having the initial intaglio of the die in the bottom thereof so that the diamonds will each register with its respective depression.

binder carrying the diamonds holds them in their exact location, and when the pressure is applied, each diamond is forced to the bottom of its respective depression in the mold, while the metal of which the binder is composed is 'practically homogeniously united with the metal of the casting, losing its identity entirely in the heated plastic metal which latter surrounds every interstice of the diamonds, forming an almost perfect bond therewith and holding them in the exact locations as originally indicated on the pattern. The electroplating deposit which encases each stone serves also to protect the stone during the first impact of the plastic or molten metal in the casting process, and provides a cushion therefore'while being melted and losing its identity in, and during contraction of the casting metal about said diamondsin cooling.

In some instances it may be desirable to set the diamonds in the finished bit flush with the face thereof, and in which case the individual depressions are omitted from the mold. Notwithstanding this, the electroplated deposit will hold the diamonds in their exact locations during the pressure casting process, the only diiference being that the diamonds will be fiush with the face of the bit and not protrude as in the hereinbefore mentioned process. A bit having the diamonds flush with the face and the clearance surfaces is illustrated in Figures 4 and 5.

when this method of forming the bits is employed an impression is made in wax of the face of the bit desired and the stones are placed therein and a binder film of metal electroplated thereover, all as previously described, and it will be understood that the surfaces of the marginal. diamonds projecting from the wax impression will also be completely covered with the electroplated metal. This results in the width of the thus provided electroplated metal annulus surrounding the diamonds being just the predetermined dimension greater than that of the body portion of the bit head of which it ultimately becomes a part during the pressure casting process to provide the desired clearance, and this difference in diameter is clearly shown in Figures 4 and 5, wherein the inner and outer walls of the bit head are illustrated at 5 and 6 respectively. In this manner ample clearance for both the inner and outer walls of the bit are provided, and this clearance cooperates uniformly with the radial channels illustrated at I transverse the cutting face and inner and outer walls thereof of the bit, and intermediate of which channels any desired grouping of bortz may be arranged. The only difference between this method of forming the bits and that first described is that the bottom of the mold is not formed with a depression for each diamond cast in the face of the bit; otherwise the methods are identical.

In Figure 3 it will benoted that the slug or die segment is illustrated as being somewhat elongated, which may be preferred in a modified method of forming the bits.

It is quite evident from the foregoing that in metal from above 'tially of said bit to provide adequate clearance shaping oi the bit -metal being capable of and alloying the initial forming of the mold, the specific construction thereof may be materially modified in the art of deer pressure'casting but. without departing from the steps of the invention.

From the above it is obvious that with our method it is possible to form a plurality of bits from the same mold and die, and each bit, with the slight exception of the diflerentiation in shape oi. the diamonds or bortz cast therein, will be an exact duplicate of each other. 1 Having thus described our invention, what we claim and desire to secure by letters Patent, is: 1. The herein described method 01' forming a core drill bit having diamonds in the face thereoi, comprising the iorming'of a matrix therefor having a depression therein for each diamond, placing the diamonds within said depressions, electroplating a thin metal binder about that portion of said diamonds protruding from said matrix, placing said metal binder with said diamonds therein within a refractory mold for and forcing molten or plastic metal of which the bit is to be composed into said mold by pressure casting, said electroplated with said molten or plastic metal during said pressure casting, ;and subsequently removing surplus said diamonds circumferenin the operation of the bit.

a 2, The herein described method 01 casting a diamond core drill bit comprising treating the diamondsto render them electrically conductive,

preparing in a suitable adhesive material a pattern oi the bit iace design. placing the di amonds in said adhesive material in accord-v ;same in place, placing said forcing heated molten metal, having an aiilnity during which said molten metal.

ance' with said pattern, electroplating a thin film of metal about each diamond until each is at least partially incased in a metal coating to securely hold same in place, removing said metal film with the diamonds incased therein from the V adhesive material and placing same in a casting mold, and forcing heated plastic metal into said mold by pressure casting to form the bit, said electroplated metal film being capable ofand alloying with the heated plastic metal during said pressure casting.

3. The method of making .a diamond drill which comprises placing previously prepared diamonds or bortz each in a predetermined location, electroplating a thin film of suitable metal 15 about'said diamonds to hold same in said locations, then placing the film thus formed and containing said diamonds in a mold, then i'orcing the metal of which the drill is to ,be formed into said mold while in a heated plastic state by pressure casting, the metals of said fllm and said head having an ailinity for each other whereby said illm loses itsidentity during the pressure. casting step.

4. The method of making a diamond core drill bit which comprises electroplating a thin film of metal about a plurality of diamonds to hold film, containing laid diamonds into a pressure castingmold, then for-said electroplated metal, into said mold by pressure casting, thereby forming the bit, and

fllm loses its identity in said v EDWARD H.

wanmnraum- 

